If you wanted to find the last time Björk really let her hair down on a record, you'd have to look all the way back to 1995's Post. From "Army of Me" (its video found her driving a tank and wearing gold teeth) to "It's Oh So Quiet" to "I Miss You", that record sired some of the most vibrant songs of her career. It's a side of her we've only caught in brief glimpses ever since. In the course of moving back to Iceland after a letter bomb scare in 1997, engaging in psychological warfare with Lars Von Trier on the set of 2000's oppressively bleak Dancer in the Dark, falling in love with Matthew Barney in 2001, giving birth to her second child in 2002, and of course, just getting older, Björk's output has become increasingly austere and inward-looking. The unhinged, mischievous screamers that were once her calling card are now mostly a thing of the past, replaced by songs that more closely resemble holy moments than sing-alongs.

But in her pre-game interviews for Volta, Björk hinted that it might finally be time to flip the switch back. "All I wanted for this album was to have fun and do something that was full-bodied and really up," she told Pitchfork-- one of a handful of interviews to feature descriptors like "fun" and "poppy" and "accessible." Disappointingly, it turns out that Timbaland and the Technicolor artwork were red herrings-- Volta is not Björk's pop record. Figuring out what it is, actually, is a much more difficult task; where even her most divisive albums have managed to push her artistic boundaries, Volta feels limp and strangely empty-- almost unfinished.

Its emptiness is doubly disappointing when considering the caliber of guest performers involved. In addition to Timbaland, Volta features Antony Hegarty (of & the Johnsons fame), improv drummer Chris Corsano, Lightning Bolt drummer Brian Chippendale, Konono No. 1, Malian kora player Toumani Diabate, Chinese pipa player Min Xiao-Fen, and a 10-piece Icelandic brass band. Some of that guestlist goes wasted; Chippendale is banished to slow-build purgatory on the brooding Antony duet "The Dull Flame of Desire", while Konono No. 1 are reduced to fighting for space with 37 other elements in the already overstuffed "Earth Intruders". Even Timbaland's contributions feel oddly apathetic; aside from "Earth Intruders", which pales in comparison to any Timbaland/Björk collaboration you'd hear in your head, neither of his other productions bear much of his imprint at all. With its distorted, squelching rhythms, "Innocence" sounds, ironically, more like the work of longtime collaborator Mark Bell, and "Hope"s scampering percussion and spindly kora lines, while interesting, are marred by an atrocious lyric about terrorism: "What's the lesser of two evils?/ If a suicide bomber made to look pregnant/ Manages to kill her target or not?"

For a record ostensibly about tribalism and reconnecting with our animal sides, much of Volta plods. Insulated with samples of running water, long, mournful horns, and gently plucked pipa, "I See Who You Are" is a tranquil lullaby without much of a melody at all. "Vertebrae by Vertebrae" rests on a looped horn sample not far from Peter Thomas' "Bolero on the Moon Rocks" (sampled by Pulp on "This Is Hardcore"), but Björk can't take it anywhere, instead filling its five minutes with runs from her catalog of preferred vocal shorthand scribbles. On the heels of those two songs, the rhythmless "Pneumonia"-- which finds Björk utterly adrift melodically-- is an even harder sell.

There are, of course, a handful of lovely parts as well. While I have problems with the way "Earth Intruders" sounds-- muddy, clunky, overcompressed, and not nearly as aerodynamic as you'd expect a Björk/Timbaland track to sound-- its charm comes through with time. With lyrics pulled from a Russian poem made popular by Andrei Tarkovsky's Stalker (how's that for pop!) and regal, curling horns reminiscent of the crescendoing strings in Henryk Gorecki's 3rd Symphony (uh, ditto), the 7½-minute Björk/Antony duet "The Dull Flame of Desire" is a darkly elegant setpiece that beautifully showcases both voices. Ultimately, though, it's the industrial jackhammering of "Declare Independence" that steals the show. Built around a wriggling synth lead, some brash EQing, and white-hot swaths of digital noise, it's a gloriously messy few minutes-- one of her most transcendent tracks to date.

In the end, though, those golden moments are too few and far between, and the slow, unfurling, lingering moments too long. If the critical and fan response to this album reflects that of the fascinatingly eccentric (but largely maligned) Medúlla, I'll be curious to see how she responds. Until then, Volta is mostly proof that Björk is as fallible as the messy, unpredictable humanity she celebrates, and that even her definition of "pop" is avant-garde.